Temperature control apparatus employing heating and cooling control circuits arranged in a head to toe configuration

ABSTRACT

The present system is a time proportional system for controlling both heat and cooling. The present system provides a plurality of stages of individual heating control circuits and a plurality of stages of individual cooling control circuits. The system in general follows a last on-first off procedure. The ascending stages of the heating series are respectively circuitry connected to the descending stages of the cooling series, i.e., the first stage of the heating series is connected to the last stage of the cooling series and vice versa so that when a heating stage is turned on it will cause the cooling stage to which it is connected to be turned off and vice versa. Because of the head to toe arrangement the present system can employ both heating and cooling stages simultaneously when the conditions warrant such an arrangement.

United States Patent 1 [111 3,730,819 Evalds [451 May 1, 1973TEMPERATURE CONTROL Primary Examiner-CharlesSukalo APPARATUS EMPLOYINGHEATING AND COOLING CONTROL CIRCUITS ARRANGED IN A HEAD TO TOECONFIGURATION [75] lnventor: Egils Evalds, Ardmore, Pa.

[73] Assignee: Athena Controls, Inc., West Conshohocken, Pa.

[22] Filed: Oct. 18, 1971 [21] App]. No.: 189,881

[52] US. Cl ..165/26, 165/30 [51] Int. Cl ..F25b 29/00 [58] Field ofSearch ..165/26, 27, 30, 12

[56] References Cited UNITED STATES PATENTS 3,677,335 7/1972 Weathouston..165/12 Att0rneyWilliam E. Cleaver [57] ABSTRACT The present system isa time proportional system for controlling both heat and cooling. Thepresent system provides a plurality of stages of individual heatingcontrol circuits and a plurality of stages of individual cooling controlcircuits. The system in general follows a last on-first off procedure.The ascending stages of the heating series are respectively circuitryconnected to the descending stages of the cooling series, i.e., thefirst stage of the heating series is connected to the last stage of thecooling series and vice versa so that when a heating stage is turned onit will cause the cooling stage to which it is connected to be turnedoff and vice versa. Because of the head to toe arrangement the presentsystem can employ both heating and cooling stages simultaneously whenthe conditions warrant such an arrangement.

8 Claims, 1 Drawing Figure Patented May 1, 1973 INVENTOR EGILS EVALDS AT TORNE Y TEMPERATURE CONTROL APPARATUS EMPLOYING HEATING AND COOLINGCONTROL CIRCUITS ARRANGED IN A HEAD TO TOE CONFIGURATION DESCRIPTION Thepresent invention relates to a temperature control system and inparticular to a system which timeproportionately controls both heatingand cooling of a large volume of air or controls a system which requiresan overlap of heating and cooling efforts.

When a heating or cooling effort is effected by electrical power it isvery often desirable to accomplish such an effort by incrementallyadding hot air and alternatively cooled air. It has become the procedureto employ a mechanical stepping switch which is stepped up to cut incertain heating elements or certain cooling elements and stepped down tocut out certain heating elements or certain cooling elements. Themechanical stepping procedure is satisfactory to a point but has certainlimitations which are overcome by the present invention. The steppersystem employs a mechanical device which involves moving parts andtherefore is burdened by the wear involved therewith. In addition, thestepper device does not lend itself to a vernier control because thesteps act to cut in or cut out a given amount of heat (or cold) eachtime they are advanced or returned. Hence, cycling for a smalldifference of temperature is not readily. accomplished withouttemperature overshoot when the stepper system is employed. Further, ifthe device of the temperature control is a large room or series of roomssuch as in a super market or the like, and there is a single controlsystem employed for both heating and cooling it is very difficult tointerconnect stepping switches to effect a control of one stepper byanother so that, for instance, the humidity control of the coolingsystem can be taken advantage of when in fact the system is attemptingto warm the room.

SUMMARY The present system comprises a plurality of stages of heatingcontrol circuits and a plurality of stages of cooling control circuitsso connected that the first heating control stage to be turned on inresponse to a signal to add heat is connected to the last coolingcontrol stage to be turned on and the next heat control stage inascending order is connected to the next succeeding descending coolingcontrol stage so that finally the first cooling control stage to beturned on is connected to the last heating control stage to be turnedon. As will become apparent in the description that follows, the abovedescribed head-to-toe arrangement enables the present system toeffectively employ both heating and cooling efforts simultaneously sothat the humidity control of the cooling device can be used when thesystem is demanding heat and further so that the system can effect acycling procedure in response to a very small change in temperature, inaddition to being able to effect a normal heating and cooling effort.The pulse generator portion of the circuit in conjunction with theheaddo-toe arrangement enable the circuit to perform a vernieroperation.

The features and objects of the present invention will become apparentin accordance with the description to follow taken in conjunction withthe drawing.

In the FIGURE there is shown a source of electrical power 11 and 12represented by the well understood symbols 8+ and B-. The source 11 and12, as depicted in the circuit shown in the FIGURE, is a direct currentsource of electrical power. Connected across the source of electricalpower 11 and 12 is a bridge circuit. The bridge circuit has inputterminals 13 and 14 and output terminals 15 and 16. Upon examination ofthe FIGURE it can be seen that one leg of the bridge is represented bythe resistor 17, a second leg of the bridge is represented by the serialconnection of the thermistor 18, the set point resistor 19 and the fixedresistor 20. Also upon inspection of the FIGURE it can be seen that thethird leg of the bridge is represented by the resistor 21, while afourth leg of the bridge is represented by the serial connection of thefixed resistor 22 and the fixed resistor 23. Accordingly, when thesystem is in operation and power is supplied to the terminals 13 and 14there is current flow from the terminal 13, through the resistor 17,through the resistors 18, 19 and 20 to the terminal 14 as well ascurrent flow through the resistor 21, through the resistors 22 and 23 tothe terminal 14.

The set point resistor 19 is the element which permits the user todetermine or set the temperature about which the system will operate.Assume for a given setting of the set point resistor 19 that thethermistor 18 is cold. In other words, the temperature of the item whichthe thermistor is monitoring is colder than the temperature value towhich the set point resistor 19 has been set. If the thermistor 18 iscold, its resistance is high and there is a relatively limited currentpassing through the resistor 17, thermistor 18 and resistors 19 and 20.Hence there is a relativelly small voltage drop across the resistor 17.With the relatively small voltage drop across the resistor 17, theterminal 15 is at a relatively high voltage and hence the transistor 24is conditioned to conduct. 1f the transistor conducts, there will becurrent flow from the terminal 13, through the resistor 25, through thetransistor 24, to the terminal 26, through the variable resistor 27,through the resistor 28, to the terminal 14. If the transistor 24 isconducting fully (i.e., has been completely turned on) there will bevirtually no current flow through the resistor 29 to charge up thecapacitor 30.

It can be determined from the FIGURE in view of the foregoingdescription, that the voltage at point 26 will be virtually the same asthe voltage on the collector of transistor 24 and hence the transistor31 will not be forward-biased for conduction. Since the transistor 31 isnot conducting, current will flow through the resistors 32 and 33 tocharge up the capacitor 34. When the capacitor 34 has been charged up toa certain percent age of the voltage which appears across the controlelement 35 and the cathode 36 of the program'unijunction transistor 37,this unijunction transistor 37 will conduct. The required voltage tofire" the program unijunction transistor 37 can vary and in thepreferred embodiment it is percent.

When the unijunction transistor 37 conducts, the capacitor 34 dischargestherethrough providing a sharp positive pulse on the add heat line 38 inresponse to the voltage developed across the resistor 39. Uponcompletion of the discharge of the capacitor 34, the program unijunctiontransistor 37 terminates its conduction and once again the capacitor 34commences to build up the charge thereon. When the proper percentage ofvoltage is developed across the capacitor 34 to fire" the programunijunction transistor 37, the unijunction transistor will fire onceagain providing a second positive pulse on the add heat line 38. Theresistor 33 and the capacitor 34 provide the RC time constant for firingthe program unijunction transistor. In other words, the period of timebetween cutting in or adding the increments of heat is determined by theRC time constant developed by the resistor 33 and the capacitor 34.

Before considering the response of the system to the positive pulses onthe add heat line 38, it should be noted that the power circuit 40 isconnected to the control circuit 41 by six terminals 42 through 47. Theterminal 42 connects the positive side of the power supply to thecooling stages, while the positive side of the power supply is connectedto the heating stages through the terminal 47. The cooling stages of thecircuit are connected through terminal 43 to the negative side of thepower supply while the heating stages are connected through terminal 46to the negative side of the power supply. The add cooling line 48 isconnected through the terminal 44 to the bridge circuit while the addheat line 38 is connected through the terminal 45 to the bridge circuit.

Further before considering the effect of positive pulses appearing online 38, consider the structure of the heating and cooling stages. Theresistors 49, 50 and 51 represent the load elements of the heaterstages. In other words, the resistors 49, 50, 51 represent either theheaters themselves, as the case in the small systems, or relays (or someother type switch) through which the heaters are activated to actuallygenerate heat. The resistors 52, 53 and 54 are the load resistors of thecooling circuits. These last mentioned load resistors represent therelays which turn on the cooling compressors and activate the deviceswhich actually add cool air to the room or item to be cooled.

Assume that none of the heating devices has been turned on and none ofthe cooling devices has been turned on and that the system is initiallystarting up. Under these circumstances current will flow from terminal13, along line 55, through resistor 49, through resistor 56, throughcapacitor 57 (which is becoming charged), through the resistor 58, toline 59 across the resistor 23 to terminal 14. The combined resistanceof the resistors 49, 56, and 58 is sufficiently high to limit currentflow so that the silicon controlled rectifier 60 does not get turned onwhen the capacitor 57 is being charged up. At the same time there iscurrent flow from the terminal 13, along line 55, through the resistor50, through the resistor 61, through the capacitor 62 (which is beingcharged), through the resistor 63, to line 59, across the resistor 23 tothe terminal 14. In a similar manner, the resistors 50, 61 and 63 are ofsufficiently high resistance to limit the current flow so that in thecourse of charging up the capacitor 62 the silicon controlled rectifier64 does not get turned on. It should be noted that on the heating side,the capacitor 65 is not charged in response to this initial turn-onactivity.

At the same time there will be current flow from the terminal 13, alongthe line 66, through the resistor 53, through the resistor 67, throughthe capacitor 68 (which is being charged at this time), through theresistor 69, to line 70, across resistor 20, to the terminal 14. Theresistors 53, 67 and 69 are sufficiently high to limit the current flowthereacross so that the silicon controlled rectifier 71 is not turned onwhen the capacitor 68 is being charged. At the same time there iscurrent flow from the terminal 13, along the line 66, through theresistor 54, through the resistor 72, through the capacitor 73 (which isbeing charged at this time), through the resistor 74 to line 70, throughthe resistor 20 to the terminal 14. As was true with the other circuitarrangements, the resistors 54, 72 and 74 are of sufficiently highresistance, to limit the current flow so that the silicon controlledrectifier 75 is not turned on when the capacitor 73 is being charged. Itshould be noted that the capacitor 76 is not charged up in response tothis initial turn-on activity.

Reconsider now that the thermistor 18 is colder than the value set onthe resistor 19 so that there is a positive pulse applied to the addheat line 38 as was described earlier in response to the discharge ofthe capacitor 34. When a positive pulse appears on the add heat line 38there is current flow through the diode 77 to charge the capacitors 65.As was explained above, the capacitor prior to this time had beendischarged and hence it passes the positive pulse to provide a positivebias to the silicon controlled rectifier 78. Accordingly the siliconcontrolled rectifier 78 conducts. At the same time the capacitor 65ischarged by the current flow through the resistor 79 but discharges whenthe positive pulse on line 38 subsides. It should also be noted thatwhen the silicon controlled rectifier 78 conducts there is current flowfrom terminal 13, along the line 66, through the resistor 52, along theline 84 to charge the capacitor 82 as shown by the polarity symbolsthereon. At the same time it should also be noted that the capacitor 57discharges through the resistor 56, through the conducting siliconcontrolled rectifier 78, through the resistor 58 to the other side ofthe capacitor 57. Hence, the capacitor 57 is in a discharged state andis able to respond to the next positive pulse on line 38. If we assumethat thermistor 18 remains colder than the value set on the resistor 19then the capacitor 34 will have a chance to charge up a second time andfire the unijunction transistor 37 so that a second positive pulse willbe generated on line 38. The second positive pulse on line 38 istransmitted through the diode 85, through the capacitor 57, to turn onthe silicon controlled rectifier 60. When the silicon controlledrectifier 60 is turned on, there is current flow from the terminal 13,along the line 66, through the resistor 53, along the line 86, to chargeup the capacitor 87, in accordance with the polarity symbols shownthereon. At the same time the capacitor 62 is discharged through theresistor 61, through the conducting silicon controlled rectifier 60,through the resistor 63to the other side of the capacitor 62. As wasdiscussed earlier in connection with the capacitor 65, the capacitor 57will be discharged after the second positive pulse disappears. The nextpositive pulse will be passed through the capacitor 57 but will have noeffect on the silicon controlled rectifier 60 because that siliconcontrolled rectifier is already conducting. The method by which the laststage silicon controlled rectifier 64 is turned on is similar to themethod just described and no further description thereof appears to benecessary.

It must be remembered that when the silicon controlled rectifier 78 wasturned on, current flowed through the resistor 49. The current flowingthrough the resistor 49 (which in this case will be assumed to be thewinding of a relay) caused a relay to be energized which turned on thefirst heat generating device, represented by, or associated with, thefirst stage heating control circuit. Similarly when the silicon controlled rectifier 60 was turned on, a second stage of heat was turned onand thus two heating sources were generating heat for the device to betemperature controlled. Similarly, when the third stage siliconcontrolled rectifier 64 is turned on, a third stage or third heatgenerating device is turned on, represented by the resistor 51.

Consider now that the thermistor 18 has become sufficiently warm so thatthe current therethrough has been limited and hence the transistor 24 isno longer conducting or is conducting very little. Accordingly, thepoint 16 becomes positive with regard to the terminal 26 and hence thetransistor 31 commences to conduct heavily. Under these circumstancesthere would be current flow through the resistor and resistor 29 tocharge up the capacitor 30 and when a sufficient amount of charge hasbeen developed across the capacitor 30, the unijunction transistor 90conducts to provide a positive signal on the line 48 in accordance withthe voltage developed across the resistor 91. When this add cold pulseis generated on line 48 it is transmitted through the diode 92, throughthe capacitor 76, to turn on the silicon controlled rectifier 93. Itshould be noted that the first stage of the cooling control series is atthe opposite end of the chain from the first stage of the heatingcontrol series. When the silicon controlled rectifier 93 conducts, theterminal 94 becomes negative and hence the potential developed acrossthe capacitor 88 (as shown in the FIGURE) is measured from a negativepotential thus making the terminal 95 become very negative therebyturning off the silicon controlled rectifier 64. It should be apparentthen that when the first stage of the cooling element gets turned on itsacts to turn off the last stage of the heating element if in fact thatlast stage is conducting. It should also be apparent that the capacitor88 will charge up in the direction opposite from the polarity shown inthe FIGURE. The capacitor 76 will not 1 remain charged once the positivepulse has disappeared and any further positive pulses will have noeffect so long as the silicon controlled rectifier 93 is conducting. ltshould also be noted that when the silicon controlled rectifier 93conducts the capacitor 73 discharges therethrough, thereby putting thatcapacitor in a state to respond to the next positive signal on line 48.If we assume that the thermistor 18 has not cooled off sufficiently andthat therefore the transistor 31 continues to conduct, then thecapacitor 30 will charge up a second time and fire the programunijunction transistor 90 a second time thereby providing a secondpositive pulse on line 48. The second positive pulse on line 48 will betransmitted through the diode 96, through the capacitor 73, to turn onthe silicon controlled rectifier 75. When the silicon controlledrectifier 75 conducts, the terminal 97 goes negative and hence thecharge across the capacitor 87 is measured from a negative potential,causing the terminal 98 to go very negative thereby turning off thesilicon controlled rectifier 60. Ac-

cordingly it becomes apparent that when the second stage of the coolingseries is turned on it acts to turn off the second stage heating circuitprovided that last mentioned circuit has been conducting. At the sametime the capacitor 87 charges up in .a direction opposite from thatshown in the drawing. it should be remembered that during the turning onof the first and second stages of the cooling system that the resistors54 and 53 which are the load resistors can act to energize relays whichin turn can activate compressors and fans to pump cool air into the roomor device being temperature monitored. The turning on of the last stagesilicon controlled rectifier 71 is similar to those previously describedand its turning on acts to turn off the first stage of the heatingcontrol circuits if that stage has been conducting. Capacitor 82 chargesup in the opposite direction from that shown in the FIGURE.

It can be determined by examining the circuit that as each heating stageis turned off, the associated control capacitor. which links it to thenext stage becomes charged so that the last stage turned off would bethe first stage turned on, if the system should again generate apositive pulse on line 38. For instance, when the silicon controlledrectifiers 64 and 60 have been turned off the capacitor 62 will becharged up thereby preventing the silicon controlled rectifier 64 fromturning on in response to the generation of a positive pulse on line 38.However, the capacitor 57 would not be charged up since the siliconcontrolled rectifier 58 is still conducting. Hence, if after the timethat the silicon controlled rectifiers 64 and 60 were turned off, apositive signal appeared on line 38 the capacitor 57 would respond tothat signal to turn on the silicon controlled rectifier 60. lt should beapparent that the system follows the pattern that the last stage turnedoff is the first stage turned on. An examination of the cooling controlstages will reveal that the last stage turned off is the first stageturned on.

With respect to the utility of the present control circuit arrangementconsider the following. If the system is controlling the heating andcooling of a large room such as a supermarket or church auditorium orthe like, the comfort of the shoppers, parishioners or the like is theprime consideration. If only heat is needed the system incrementallyadds heat and the electrical system is not overburdened. If only coolingis needed, the system incrementally adds cold air and the electricalsystem is not overburdened. However, on many occasions heat is suppliedand with the addition of the body heat of either the shoppers or theparishioners or the like, the temperature and the relative humidity ofthe "room" increases. In many systems the only solution to this problemis to turn off the heat until the temperature decreases by some"natural" process. Such a solution takes a long time and under suchcircumstances the relative humidity makes the temperature of the roommost uncomfortable, until the comfort index is arrived at. In thepresent system when the heat exceeds the value set on resistor 19 theresistance of the thermistor 18 decreases to a point where there is apositive pulse generated on line 48. This add-cool air signal (positivepulse) serves to turn on the silicon controlled rectifier 93 as justdescribed and hence the load resistor 54 would be energized and therebypicking up a relay cutting in a first compressor to add cool air to theroom being monitored. This last action accomplishes two things. Thetemperature of the room is positively reduced rather than waiting for anatural" cooling process, and at the same time the humidity is alsoreduced. The alternative as mentioned above is to permit the room tocool off naturally and add a de-humidifier which means the addition ofequipment at some obvious increased cost. While it may seem aninefficient operation to be getting cool air at the same time that thesystem is adding hot air, the system is effective with this procedure inthe sense that the shoppers comfort or parishioners comfort (withrespect to temperature and humidity) is attained in a very short time.In short, the present system makes use of the already existing coolingsystem to immediately control the temperature and humidity and thecooling system is an already existing necessary part of the overallsystem for controlling the temperature in the summer months. If in factin this first hypothetical situation the temperature remains warmdespite the emission of the cool air from the first cooling stage, asecond pulse is generated on line 48 and a second cooling device throughresistor 83 would be cut in" to add additional cooled air and to reducethe humidity of the room. If this additional cool air should reduce thetemperature of the room and hence the temperature of the thermistor 18to a value below the value set on the resistor 19 then an additional addbeat signal (positive pulse on line 38) would be generated to once againturn on the silicon controlled rectifier 60.

It should be clearly understood that while there are shown but threestages of heating and but three stages of cooling, the system couldobviously have many stages depending upon the amount of cooling andheating to be used. This particular system is very useful in heatinglarge rooms such as supermarkets, church auditoriums, athletic fieldhouses, and things of this kind, because of the heating and coolingwhich take place throughout the summer and winter months and because theequipment can be effectively used to control humidity as well astemperature at any season of the year.

Another feature of the present invention is the vernier control of thesystem. As mentioned earlier, if a stepper is used and heat is required,a heating unit gets turned on with very little opportunity to have itoverlap with a cooling unit. If we consider for the moment that asupermarket or a church auditorium represents a large mass of air to beheated or cooled or to be simply kept at a comfortable temperature thenit becomes apparent that this mass of air cannot be changed rapidly withrespect to its temperature-humidity combination (often referred to asthe comfort index). Assume for a second hypothetical that the air in thesupermarket is at about the proper temperature and humidity for theshoppers comfort. Further assume that the system continually addspercent fresh air from the atmosphere which surrounds the building andin this particular situation the air being added is cold and damp. Underthese circumstances, the fresh air being brought in is adding adisproportionate amount of humidity and cold temperature. Accordingly,this air should be warmed and should be partially dried out. If nothingis done except to pass the air through a heating system then theincoming air will continually add humidity so that the room will soonbecome uncomfortable. On the other hand, if the air is dried out bycirculating it continually through the cooling system then the air inthe supermarket is apt to be cooled off below a desirable level. Theoptimum would be to have the air moderately warmed and moderately driedout and to have the system cycle its heating and cooling system toaccomplish this warming and drying of the incoming air. if in thissecond hypothetical the situation is such that the room needs the firsttwo stages of heat turned on in order to keep the room warm against theambient temperature (the temperature outside of the building) then thesystem will simply cycle the third heating stage and the first coolingstage to effectively warm the incoming air and to dry the incoming air.

It will be noted that when the silicon controlled rectifiers 78 and areconducting, the voltage across the resistor 23 is increased so that theterminal 46 is at a higher voltage value than it would be under thecircumstances when the silicon controlled rectifiers 78 and 60 are notconducting. Accordingly, the voltage at point 16 is at a relatively highvalue and hence the transistor 31 is conducting to some degree. Withtransistor 31 conducting and depending upon the degree of its conductionit will take more time for the capacitor 34 to charge up than whentransistor 31 is not conducting. Hence it will take more time to producean additional pulse on line 38. In this regard, the system isanticipatory. That is to say the system is anticipating that there willbe less heat required and is slowing down the period of the pulses to agreat measure. The anticipatory feature is on the cooling side also andis effected through the resistor 20.

In our second hypothetical we have determined that it would be desirableto turn on the silicon controlled rectifier 64 for a short period oftime and thereafter turn on the silicon controlled rectifier 93 for ashort period of time, thereby effecting a warming of the added air andalso a drying out of the added air. If the temperature of the room is ata temperature which is comfortable then the temperature of thermistor 18should theoretically be at the value set on the set resistor 19.Accordingly, both the transistors 24 and 31 should be conducting so thatthere will be no pulses created on either lines 48 or 38. However, underthis second hypothetical we have decided that we do want the siliconcontrolled rectifier 64 to conduct for a short period of time and thesilicon controlled rectifier 93 to conduct for a short period of time.The way this is accomplished is by adjusting the resistor 27. If theresistance of the resistor 27 is increased then the voltage at the point26 is increased and hence the conduction through transistors 31 and 24is reduced thereby providing some current to charge up, respectively, tocapacitors 34 and 30. The period of their charge up can be adjustedthrough the variable resistor 27. Hence we can take the system when itis at a balanced bridge condition and adjust it so that it will cyclethe last stage of the heating system and the first stage of the coolingsystem. It should be apparent that if the transistors 31 and 24 arecaused to conduct less by the adjustment of the resistor 27 thenperiodically there will be pulses generated on line 38 and on line 48,to turn on the last stage of the heating system and to also turn on thefirst stage of the cooling system. Because the first two stages of theheating system are conducting and the voltage at point 46 is increasedthe adjustment of the resistor 27 will not create an even period withrespect to charging up the capacitors 34 and 30. In other words, itwould appear that it would take longer under the circumstances for thecapacitor 34 to become fully charged than it would take for thecapacitor 30 to become fully charged. However, the system takes thisinto account because as soon as the first stage of the cooling seriesgets turned on the voltage at point 43 increases which in turn causesthe transistor 24 to conduct harder and reduces the current to charge upof the capacitor 30 (and therefore lengthens the period). The user canadjust the resistor 27 until the cycling time appears to be the propercycling time for any given set of circum stances outside of the buildingand in view of the fresh air being added to the system. This cyclingadjustment is a fire" adjustment and accordingly is termed a vernieradjustment.

In many applications I have found that it is preferable to cycle unitswhich are one stage apart. This condition gives an actual overlap ofcool air and hot air being added at the same time and provides a verycomfortable condition in the room. In order to accomplish cycling oneunit apart, and only by way of example, I employed the resistor 53 asstrictly a load resistor, i.e., current passing therethrough would notactivate a compressor. In a similar fashion I would employ the resistor51 as strictly a load resistor, i.e., current passing therethrough wouldnot activate a heating unit. Under these circumstances, it can bereadily understood that if the room was at the proper temperature withthe first two stages of heating units turned on, i.e., resistors 49 and50 having current therethrough and if the percent fresh air wasproviding an uncomfortable amount of humidity and add-cold signal wouldbe generated to turn on load 54. Hence, one cooling unit would be cutin. However, no heating unit was cut out. Therefore, the cooling unitacts to reduce the humidity while the heating units continue to heat theair. Now as the temperature starts to cool with load 54 operating an addheat signal will be generated to turn on load 51 which simply turns offthe compressor associated with load 54 but does not add any heat so thatthere is no heating over-ride.

On the other hand if the compressor associated with load 54 was notsufficiently cooling the room a second add-cold signal would activateload 53. This action would merely turn off the heater associated withload 50 but not add any cooling effort.

Accordingly small temperature and humidity swings" can be maintained bycycling between unassociated units with employing the dummy loads, i,e.,simply resistance loads. Now it should be understood that additionalstages of this type of cycling can be employed and differentarrangements of the dummy loads can be employed.

lclaim:

l. A temperature control system employing N stages of heating units andN stages of cooling units comprising in combination: a source ofelectrical power; temperature responsive circuit means; add-heat signalgenerating means connected to said temperature responsive circuit meansto produce add-heat signals in response to predetermined temperatureconditions;

add-cold signal generating means connected to said temperatureresponsive circuit means to produce addcold signals in response topredetermined temperature conditions; N heating stages arranged inascending order, with respect to said temperature responsive circuitmeans, from the first stage through the Nth stage, each heating unitstage, excepting the first stage, formed to be turned on in response tothe coincidence of an add-heat signal applied thereto and the presenceof its preceding heating unit stage being turned on, said first stageheating unit formed to be turned on in response to an add-heat signalonly; N cooling unit stages arranged in descending order, with respectto said temperature responsive circuit means, from the Nth stage throughthe first stage, each cooling unit stage, excepting the first stage,formed to be turned on in response to the coincidence of an add-coolsignal applied thereto and the presence of its preceding cooling unitstage being turned on, said first stage cooling unit formed to be turnedon in response to an add-cool signal only; first circuitry meansconnecting said N stages of heating units to said addlheat signalgenerating means; second circuitry means connecting said N stages ofcooling units to said add-cool signal generating means; and thirdcircuitry means respectively connecting each cooling unit stage indescending order to a heating unit stage in ascending order so that theNth stage cooling unit is connected to the first stage heating unit andso that the first stage cooling unit is connected to the Nth stageheating unit, said third circuitry means formed to cause a heating unitstage to be turned off when the cooling stage connectedl thereto isturned on and alternatively to cause a cooling unit stage to be turnedoff when the heating unit stage connected thereto is turned off.

2. A temperature control system according to claim I wherein saidtemperature responsive circuit means is a bridge circuit having athermistor connected in one leg thereof.

3. A temperature control system according to claim 1 wherein saidtemperature responsive circuit means has first and second inputterminals and first and second output terminals and wherein said addsignal generating means comprises a transistor having an input element,an output element and a control element, said input element connected tosaid first input terminal, said output element is fourth circuitryconnected to said second input terminal, and said control elementconnected to said first output terminal and further wherein said addsignal generating means includes a capacitor connected between saidinput element of said last mentioned transistor and said second inputterminal, and wherein said add signal generating means further include acurrent switching means connected to discharge said last mentionedcapacitor in response to a predetermined voltage developed thereacrosswhereby an add signal is generated each time said last mentionedcapacitor is charged.

4. A temperature control system according to claim 1 wherein saidtemperature responsive circuit means has first and second inputterminals and first and second output terminals and wherein saidsubtract signal generating means includes a transistor having an inputelement, an output element, and a control element and wherein said inputelement is connected to said first input terminal, said output elementis fourth circuitry connected to said second input, said control elementis connected to said first output terminal, and further wherein saidsubtract signal generating means includes a capacitor connected betweensaid input element of said last mentioned transistor and said secondinput terminal, wherein there is further included a current switchingmeans connected to discharge said last mentioned capacitor in responseto a predetermined voltage developed thereacross whereby a subtractsignal is generated each time said last mentioned capacitor discharges.

5. A temperature control system according to claim 4 wherein saidcurrent switching means is a program unijunction transistor and whereinthere is further included cross coupling circuitry between said lastmentioned program unijunction transistor and said add signal generatingmeans to prevent said last mentioned program unijunction transistor andsaid add signal generating means from turning on at the same time.

6. A temperature control system according to claim 2 wherein there isfurther included in said bridge circuit means a variable resistor whosedifferent resistance values are equated to different temperature valuesand whose setting determines the relationship between the desiredtemperature about which the system operates and the voltages developedat the output means of said bridge circuit.

7. A temperature control circuit according to claim 1 wherein said addsignal generating means and said subtract signal generating means arecommon connected through variable resistance means whereby the currentthrough said add signal generating means and said subtract signalgenerating means can be varied to generate add and subtract pulses at adifferent rate in accordance with said variable resistance setting.

8. A temperature control system according to claim 1 wherein certain ofsaid heating unit stages are formed to be simply an electrical load andnot provide heat and wherein certain of said cooling unit stages areformed to be simply an electrical load and not provide cooling.

1. A temperature control system employing N stages of heating units andN stages of cooling units comprising in combination: a source ofelectrical power; temperature responsive circuit means; add-heat signalgenerating means connected to said temperature responsive circuit meansto produce add-heat signals in response to predetermined temperatureconditions; add-cold signal generating means connected to saidtemperature responsive circuit means to produce add-cold signals inresponse to predetermined temperature conditions; N heating stagesarranged in ascending order, with respect to said temperature responsivecircuit means, from the first stage through the Nth stage, each heatingunit stage, excepting the first stage, formed to be turned on inresponse to the coincidence of an add-heat signal applied thereto andthe presence of its preceding heating unit stage being turned on, saidfirst stage heating unit formed to be turned on in response to anadd-heat signal only; N cooling unit stages arranged in descendingorder, with respect to said temperature responsive circuit means, fromthe Nth stage through the first stage, each cooling unit stage,excepting the first stage, formed to be turned on in response to thecoincidence of an add-cool signal applied thereto and the presence ofits preceding cooling unit stage being turned on, said first stagecooling unit formed to be turned on in response to an add-cool signalonly; first circuitry means connecting said N stages of heating units tosaid add-heat signal generating means; second circuitry means connectingsaid N stages of cooling units to said add-cool signal generating means;and third circuitry means respectively connecting each cooling unitstage in descending order to a heating unit stage in ascending order sothat the Nth stage cooling unit is connected to the first stage heatingunit and so that the first stage cooling unit is connected to the Nthstage heating unit, said third circuitry means formed to cause a heatingunit stage to be turned off when the cooling stage connected thereto isturned on and alternatively to cause a cooling unit stage to be turnedoff when the heating unit stage connected thereto is turned off.
 2. Atemperature control system according to claim 1 wherein said temperatureresponsive circuit means is a bridge circuit having a thermistorconnected in one leg thereof.
 3. A temperature control system accordingto claim 1 wherein said temperature responsive circuit means has firstand second input terminals and first and second output terminals andwherein said add signal generating means comprises a transistor havingan input element, an output element and a control element, said inputelement connected to said first input terminal, said output element isfourth circuitry connected to said second input terminal, and saidcontrol element connected to said first output terminal and furtherwherein said add signal generating means includes a capacitor connectedbetween said input element of said last mentioned transistor and saidsecond input terminal, and wherein said add signal generating meansfurther include a current switching means connected to discharge saidlast mentioned capacitor in response to a predetermined voltagedeveloped thereacross whereby an add signal is generated each time saidlast mentioned capacitor is charged.
 4. A temperature control systemaccording to claim 1 wherein said temperature responsive circuit meanshas first and second input terminals and first and second outputterminals and wherein said subtract signal generating means includes atransistor having an input element, an output element, and a controlelement and wherein said input element is connected to said first inputterminal, said output element is fourth circuitry connected to saidsecond input, said control element is connected to said first outputterminal, and further wherein said subtract signal generating mEansincludes a capacitor connected between said input element of said lastmentioned transistor and said second input terminal, wherein there isfurther included a current switching means connected to discharge saidlast mentioned capacitor in response to a predetermined voltagedeveloped thereacross whereby a subtract signal is generated each timesaid last mentioned capacitor discharges.
 5. A temperature controlsystem according to claim 4 wherein said current switching means is aprogram unijunction transistor and wherein there is further includedcross coupling circuitry between said last mentioned program unijunctiontransistor and said add signal generating means to prevent said lastmentioned program unijunction transistor and said add signal generatingmeans from turning on at the same time.
 6. A temperature control systemaccording to claim 2 wherein there is further included in said bridgecircuit means a variable resistor whose different resistance values areequated to different temperature values and whose setting determines therelationship between the desired temperature about which the systemoperates and the voltages developed at the output means of said bridgecircuit.
 7. A temperature control circuit according to claim 1 whereinsaid add signal generating means and said subtract signal generatingmeans are common connected through variable resistance means whereby thecurrent through said add signal generating means and said subtractsignal generating means can be varied to generate add and subtractpulses at a different rate in accordance with said variable resistancesetting.
 8. A temperature control system according to claim 1 whereincertain of said heating unit stages are formed to be simply anelectrical load and not provide heat and wherein certain of said coolingunit stages are formed to be simply an electrical load and not providecooling.